Rubicon Diff Oil Consensus

[mwilk012]

75W-85 is the OEM spec front & rear for the Rubicon, which is what I've stuck with (but have switched to aFe covers and Redline gear oil).

A thinner gear oil isn't just thrown in randomly by the factory, it's specified by the engineers in cooperation with Dana, which then builds the assemblies to spec (also quite likely different than their aftermarket units or rebuild kits offered).

People have their own opinions and are free to make their own decisions, but mine personally is to run high-quality fluids that meet OEM weight requirements.

Great, the OEM is Dana, and they specify 75W-140.

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[Kracka]

Great, the OEM is Dana, and they specify 75W-140.

They spec if for their aftermarket and rebuilt units, not the OEM unit specifically. They build OEM units to spec for Jeep which does differ, and then back if with a warranty.

Again, run whichever weight you prefer as I have zero skin in the game and merely stated factual OEM specifications (as it was previously misstated in this thread by others).

 

[azwjowner]

They spec if for their aftermarket and rebuilt units, not the OEM unit specifically. They build OEM units to spec for Jeep which does differ, and then back if with a warranty.

Again, run whichever weight you prefer as I have zero skin in the game and merely stated factual OEM specifications (as it was previously misstated in this thread by others).

No, they spec it for the OEM units: https://d3qx1uccksbb2n.cloudfront.net/docs/SPECSHEET-JL-REAR-UD44A-D44A-42019.pdf

Those include the rebuild spec for the m220 that comes on a JL. Rebuild means you're servicing the axle - it doesn't mean some variant axle other than what comes on the JL.

 

[Kracka]

Correct, exactly as I've stated, for rebuilt units.

 

[mwilk012]

Correct, exactly as I've stated, for rebuilt units.

you have no idea what you’re talking about.

 

[Lionel Hutz]

Correct, exactly as I've stated, for rebuilt units.

you have no idea what you’re talking about.

Now it’s officially an oil thread

 

[mwilk012]

Now it’s officially an oil thread

Every thread on every forum ever

 

[SCJeeps]

Understand that the oil specification is for the “system” which has compromises for each component in the system. In this case the bearings and hypoid gears. What works for one component may not be the optimal for another.
I used to work for the company that supplies the tapered roller bearings for the JL differential, mainly the tapered bearings on the pinion shaft. I actually worked in the functional test lab and recall testing these bearings. Moving up to the heavier weight oil (140) caused the bearing test stand to run and operate at a higher temperature under the same conditions. This makes logical sense as the heavier weight oil caused more drag in the bearings. So in this case while a heavier weight oil is beneficial for protecting the hypoid gearset it might not be optimal for the bearings when in consideration of heat generation. If you are towing I would just put a good quality 75w/140 synthetic in and not think about it. The OEM spec 75w/85 also works well , again I recommend a good quality synthetic. The key is to use quality synthetics and change the oil as necessary to keep contaminates out (water, mud, dirt, etc) . Hypoid gear sets and tapered bearings in differentials have been around for going on a hundred years. My 52’ Willys with a Dana 44 runs just fine 50+ years later and they didn’t have the lubrication choices that are available today.

 

[Rsarffs]

I use Valvoline 75w140 full synthetic in rear differential. This is on a 2021 wrangler unlimited rubicon with stock 33"tires. I checked rear differential temperature with a infrared thermometer at rear cover after a 20 minute trip on freeway in 98 degree weather and the hottest spot was 141 * at the upper portion of the diff. cover. Makes me wonder how hot they get on longer trips or with heavier 35, 37, 38 tires..

 

[JesseT]

75W-85 is the OEM spec front & rear for the Rubicon, which is what I've stuck with (but have switched to aFe covers and Redline gear oil).

A thinner gear oil isn't just thrown in randomly by the factory, it's specified by the engineers in cooperation with Dana, which then builds the assemblies to spec (also quite likely different than their aftermarket units or rebuild kits offered).

People have their own opinions and are free to make their own decisions, but mine personally is to run high-quality fluids that meet OEM weight requirements.

You do realize you're talking about the same manufacturer that says the transmission fluid never needs to be changed, right? It's not just engineers and OEM's coming up with these specifications. Bean counters have a lot of influence too.

 

[CarbonSteel]

This has a limited slip additive. Is that OK to use on the Rubicon axles?

The Rubicon has electronic locking differentials and does not require limited slip additive, but it does not hurt anything by it being in there. You would be hard pressed to find a synthetic gear oil that does not have limited slip additive.

 

[bd100]

For whatever it's worth I noticed no difference in MPG when changing front and rear to 75W140 synth.

 

[Dusty Dude]

Bean counters have a lot of influence too.

Imho, way too much influence. The Bain of quality and reliability…

 

[CarbonSteel]

For whatever it's worth I noticed no difference in MPG when changing front and rear to 75W140 synth.

Without a stack of multi-million dollar testing equipment and a controlled environment with specific testing methodologies, it is not possible to detect the difference.

Your right foot, a head wind, elevation change, or a heavier load will impact MPG more than a viscosity change ever will.

 

[Speed331]

The only consences you're going to get on this thread is:
A: you need oil in the differential, &
B: You should change it on some sort of regular schedule.

All other details will be discussed/argued ad nauseam...

For the record; I use 75W/140 Valvoline every 30k miles or so...

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